Introduction: Diffusion- (DWI) and perfusion-weighted (PWI) magnetic resonance imaging are powerful tools for the evaluation of therapeutic drugs for stroke. The temporal progression of the ischemic lesion can be monitored by DWI whereas PWI can be used to follow the underlying hemodynamics. The purpose of this study was to evaluate the efficacy of a novel intra-vascular compound, polynitroxyl albumin (PNA) (SynZyme Technologies), in a transient focal cerebral ischemia model in the rat. Methods: Anesthetized Sprague-Dawley rats underwent 2 hours of middle cerebral artery occlusion (MCAO) by an intraluminal suture. Three treatment groups (N=6 per group) were studied: i) saline and ii) albumin as controls, and iii) PNA. PNA, albumin, or saline was injected i.v. at 0.5, 2, and 4 h post-MCAO (total dose = 1% body weight). DWI and PWI (bolus tracking) were performed on a GE CSI 2 T spectrometer at 0.25 (before first drug treatment), 1, 1.7, 2.3, 3, and 4 h post-MCAO. At 24 h, brain sections were stained with 2,3,5-triphenyltetrazolium chloride (TTC) to obtain an MRI-independent measure of ischemic injury. Results and Conclusion: The ability of DWI to monitor the ischemic region over time revealed different evolution patterns. Lesion volumes increased significantly for both the saline- and albumin groups, whereas the growth of the lesion was suppressed in the PNA group. The lesion volume (4 h DWI) in the PNA group was reduced by 63% compared to the saline group (p=0.003) and by 52% compared to the albumin group (p = 0.006). The TTC-derived lesion volumes at 24 h are in reasonable agreement with the DWI at 4 h. The perfusion measurements suggest that improved blood flow pre- and post-reperfusion may be responsible for the beneficial effect of PNA.